Produced water has value as a source of water and as a structural material (see the Fact Sheet on Use for Hydrological Purposes). Another emerging set of uses for produced water is as a feedstock for other products. This fact sheet describes two possible uses of produced water for production of energy and chemical materials.

Geothermal Energy Production
Geothermal energy is a renewable source of energy that utilizes heat generated within the earth. Geothermal energy can be used for heating buildings or for producing electricity.

Geothermal power plants typically use hot ground water (300°F to 700°F) that is either flashed to steam or directed through a heat exchange process to heat a working fluid to vapor. The steam or vapor spins a turbine connected to a generator. Traditionally, geothermal energy developers seek out high temperature formations and construct new high-volume extraction wells to withdraw the hot ground water. In recent years, interest has shifted to finding existing sources of ground water for which the wells are already drilled. If the cost of constructing a well has already been paid for by another user, like an oil and gas producer, the geothermal power producer can use water of a lower temperature and still produce electricity economically. With this in mind, attention has shifted to evaluating operating oil and gas wells as geothermal source wells.

The first example in which geothermal power was generated from a producing oil and gas well was a test conducted at DOE’s Rocky Mountain Oilfield Technology Center (RMOTC) in Wyoming. The test unit was a 250-kW Ormat Organic Rankine Cycle (ORC) power plant. This unit was installed at the Naval Petroleum Reserve No. 3 (also known as Teapot Dome Oil Field) north of Casper, Wyoming. The ORC power unit was designed to use 40,000 bpd of 170 °F produced water from the field’s Tensleep formation to vaporize the working fluid, isopentane. The projected gross power from the unit was 180 kW (net of 132 kW). Because of the lack of sufficient cooling water for the system, an air-cooled unit was designed.

The unit was put into service in September 2008 and operated until February 2009 when the unit was shut down because of operational problems. During this period, the unit produced 586 MWh of power. The operational problems, caused by operating in excess of the unit capacity, resulted in changes in the control system and repairs to the generator/turbine system. The unit was restarted in September 2009. Between September 2009 and the end of February 2010, the unit produced 478 MWh of power at a more consistent rate than before the extended shut down (Johnson and Walker 2010).

In 2010, the Alberta Energy Research Institute provided grant funds for a geothermal power production plant to be operated at the Swan Hills oil and gas production facility in Alberta (Borealis Geopower 2010). The power production plant will use geothermal waste heat from the facility to generate electricity to be used as an alternative or supplementary source of electricity at the facility. The oil, gas and water are pumped to the surface at approximately 163 - 170 degrees F in very high volumes. The oil and gas are separated from the water, and the water is then pumped back into the formation. The project will utilize heat exchange technology to remove sufficient heat from the water before it is re-circulated to produce electricity. Southern Methodist University (SMU) has sponsored a series of conferences related to geothermal opportunities in oil fields. The SMU website[external site] contains copies of some of the presentations made at the conference.

Feedstock for Chemicals
Produced water may serve as a raw material for extraction of some chemicals. Solution mining is used to extract brine or other dissolved chemicals from underground formations. That process involves injection of water and other additives into a formation to dissolve the chemical. The chemical-laden water is then pumped back to the surface. Solution mining is energy-intensive because of the need to inject and extract large volumes of liquid. If produced water from a particular formation contains sufficient concentrations of desirable chemicals, it can be a cost-effective feedstock. The chemical producer would not have to pay for the cost of injecting water and extracting the solution – it would already be at the surface as a result of oil and gas production.

The concept of extracting chemicals is gaining interest. One chemical that has already attracted attention as a possible byproduct of produced water is lithium. Researchers in Brazil are studying the economical feasibility of extracting sodium carbonate (sodium ash) from produced water (Grimaldi 2010). Other uncommon minerals can be future targets for extraction from produced water.

Other
Another future area in which produced water could possibly play a role is as a host medium to grow algae that can subsequently used for biofuels production. As part of that process, carbon dioxide could be added to the algal cultures to stimulate their growth rate, while concurrently removing CO2 from the atmosphere.

Clark and Veil, 2009, “Produced Water Volumes and Management Practices in the United States,” ANL/EVS/R-09/1, prepared for the U.S. Department of Energy, National Energy Technology Laboratory, September, 64 pp.

Grimaldi, M.C., W.J. Castrisana, F.C. Tolfo, F.P. Christino, L.M.L. Geraldo, G.C. Saliba, and D.E.B. Lopes, 2010, “Produced Water Reuse for Production of Chemicals,” SPE 127174, presented at the SPE International Conference on Health, Safety, and Environment in Oil and Gas Exploration and Production, Rio de Janeiro, Brazil, April 12-14.